Determining tracks to release in a target volume mirrored from a source volume

ABSTRACT

Provided are a computer program product, system, and method for determining tracks to release in a target volume mirroring tracks from a source volume. Tracks received from the source volume are written to the target volume to form a consistency group of tracks in the source volume at the target volume. A determination is made of tracks available to release from a volume table providing a state of the tracks in the target volume and space allocated to the determined tracks is released. A point-in-time copy of the target volume is crated and complete is returned to forming the consistency group in response to releasing the space and creating the point-in-time copy.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a computer program product, system, andmethod for determining tracks to release in a target volume mirroringtracks from a source volume.

2. Description of the Related Art

Storage volumes may be “thin provisioned”, meaning that extents ofstorage space are assigned to the volume but not allocated until needed.Additional extents may be allocated to the volume on an extent boundaryat a time when an allocated extent is first written. Extents that areallocated but not being used for a “thin provisioned” volume may bereleased, i.e., unallocated, and available to assign to other thinprovisioned volumes.

The data in a thin provisioned volume may be subject to a mirror copyoperation, such as an asynchronous copy operation to a secondary volume.Data may be copied in consistency groups to provide the mirroring ofchanged data consistent as of a consistency group time. Data in theconsistency group may comprise data that has been updated in the primaryvolume prior to a time of a next consistency group.

In current systems, if a space release command is received to releasetracks within a consistency group being mirrored to a secondary volume,then the consistency group copy is cancelled to allow the space releasecommand to complete. A new consistency group may be formed to cause thecopying of all data prior to the previous consistency group formed.

Described embodiments provide improved technological solutions tooptimize computer technology related to determine space to release fortracks a consistency group in-progress of being formed.

SUMMARY

Provided are a computer program product, system, and method fordetermining tracks to release in a target volume mirroring tracks from asource volume. Tracks received from the source volume are written to thetarget volume to form a consistency group of tracks in the source volumeat the target volume. A determination is made of tracks available torelease from a volume table providing a state of the tracks in thetarget volume and space allocated to the determined tracks is released.A point-in-time copy of the target volume is crated and complete isreturned to forming the consistency group in response to releasing thespace and creating the point-in-time copy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a storage environment.

FIG. 2a illustrates an embodiment of components in a source server in astorage environment of FIG. 1 from which tracks are mirrored to a targetserver.

FIG. 2b illustrates an embodiment of components in a target server in astorage environment of FIG. 1 to which tracks are mirrored.

FIG. 3 illustrates an embodiment of source mirror copy relationshipinformation.

FIG. 4 illustrates an embodiment of target mirror copy relationshipinformation.

FIG. 5 illustrates an embodiment of point-in-time copy information.

FIG. 6 illustrates an embodiment of operations to form a consistencygroup on a target volume.

FIG. 7 illustrates an embodiment of operations to process a message thatall the tracks for the consistency group being formed have been sent.

FIG. 8 illustrates an embodiment of operations to process tracks for anew consistency group.

FIG. 9 illustrates a computing environment in which the components ofFIG. 1 may be implemented.

DETAILED DESCRIPTION

In current art, if a space release command is received to release spacethat is within a consistency group in progress of being formed as partof mirroring data to a target storage system, then the consistency groupis canceled to allow the space release command to proceed. Describedembodiments provide improvements and optimizations to the computertechnology for releasing space at a target volume of a consistency groupbeing formed as part of forming a consistency group in a mirror copyingenvironment. With the described embodiments, after forming a consistencygroup of tracks in a source volume to copy to a target volume, adetermination is made of space for tracks in the target volume torelease based on available space indicated in the volume table for thetarget volume as available to release. After completing the consistencygroup and releasing available space in the target volume, apoint-in-time copy of the target volume is created at the target server.Complete is returned to the source server for the consistency group inresponse to releasing the space and creating the point-in-time copy. Thesource server may start forming the next consistency group uponreceiving the completion message from the target server.

With the described embodiments, the target server automaticallydetermines to release space after forming the consistency group toautomatically release space at the target volume to be available for usein other thin provisioned volume. Since the target server has thecurrent information on the state of the target volume, the target servermay more efficiently determine to release space than a host system oroperator at the host system.

FIG. 1 illustrates an embodiment of a data storage environment having atleast two storage systems 100 ₁ and 100 ₂, each including storageservers 200 ₁ and 200 ₂, respectively, managing access to volumes 104 ₁and 104 ₂ configured in storages 106 ₁ and 106 ₂. Host systems (notshown) may perform read and write operations with respect to the firststorage system 100 ₁ over a storage network 110. A source storage 106 ₁may comprise a primary production volume to which hosts direct read andwrite request. The source server 200 ₁ may mirror tracks in the sourcevolumes 104 ₁ to the target storage system 100 ₂ to maintain data inconsistency groups at the target server 200 ₂. A track may comprise anydata unit type, such as a track, logical block, extent, page, etc.

When formation of the tracks for a consistency group is completed in thetarget volume 104 ₂, the target server 200 ₂ may create a point-in-timecopy 108 of the target volume 104 ₂ for the consistency group. There maybe multiple point-in-time copies at different consistency group timesfor a target volume 104 ₂.

The term “storage system” as used herein may refer to a storage server200 ₁, 200 ₂ and/or the storage 106 ₁, 106 ₂ managed by the server.

The storages 106 ₁, 106 ₂ may comprise different types or classes ofstorage devices, such as magnetic hard disk drives, solid state storagedevice (SSD) comprised of solid state electronics, EEPROM (ElectricallyErasable Programmable Read-Only Memory), flash memory, flash disk,Random Access Memory (RAM) drive, storage-class memory (SCM), etc.,Phase Change Memory (PCM), resistive random access memory (RRAM), spintransfer torque memory (STM-RAM), conductive bridging RAM (CBRAM),magnetic hard disk drive, optical disk, tape, etc. The volumes 104 ₁,104 ₂ may further be configured from an array of devices, such as Just aBunch of Disks (JBOD), Direct Access Storage Device (DASD), RedundantArray of Independent Disks (RAID) array, virtualization device, etc.Further, the storages 106 ₁, 106 ₂ may comprise heterogeneous storagedevices from different vendors and different types of storage devices,such as a first type of storage devices, e.g., hard disk drives, thathave a slower data transfer rate than a second type of storage devices,e.g., SSDs.

The storage network 110 used by the storage systems 100 ₁ and 100 ₂ tomirror data may comprise a storage network such as one or moreinterconnected Local Area Networks (LAN), Storage Area Networks (SAN),Wide Area Network (WAN), peer-to-peer network, wireless network, etc.

A volume 104 ₁, 104 ₂ may comprise any logical or physical allocation ofdata, such as a logical volume, logical unit number (LUN), logicaldevice, logical disk, etc. The volumes 104 ₁, 104 ₂ may comprise thinprovisioned volumes, meaning that tracks are only allocated in thestorage 106 ₁, 106 ₂ for a volume when needed to store data. The spacerelease operations described herein release space in the volumes 104 ₁,104 ₂ to be available for allocation to other thin provisioned volumes.

FIG. 2a shows components of the source server 200 ₁, as including aprocessor 202 ₁ and a memory 204 ₁ including programs executed by theprocessor 202 ₁ as well as a cache 206 ₁ to cache read and write datafor the source storage 106 ₁. The cache 206 ₁ may also store data beingtransferred between the servers 200 ₁, 200 ₂ as part of mirror copyrelationships. The memory 204 ₁ includes an operating system 208 ₁,which forms volumes 104 ₁ and maintains volume tables 210 ₁, such as avolume table of contents (VTOC), file allocation table, etc., providinginformation on the tracks or extents of tracks allocated to the volume104 ₁ and free space in the volume, as well as other metadata. The cache206 ₁ may store a volume table copy 210 _(C) comprising a copy of avolume table 210 as of a consistency group time to maintain a state of avolume 104 ₁ for a consistency group.

The operating system 208 ₁ may manage volumes 104 ₁ as thin provisionedvolumes and allocate space to the provisioned but unallocated space anda space release task 214 ₁ may issue commands to the device adaptors 216₁ to release space allocated to a thin provisioned volume 104 ₁ to makeavailable to assign to other volumes 104 _(j).

The memory 204 ₁ includes a source copy manager 212 ₁ to create andmanage mirror relationships 300 to mirror data in volumes 104 ₁ in thesource storage system 100 ₁ to a target volume 104 ₂ in the targetstorage system 100 ₂ as part of consistency groups. The operating system208 ₁ may further spawn one or more space release tasks 214 ₁ to processthe volume table copy 210 _(C) to determine space to release for tracksin a volume 104 ₁.

The server 200 ₁ includes one or more device adaptors 216 ₁ tocommunicate with devices in the source storage 106 ₁ and one or morenetwork adaptors 218 ₁ to communicate with the network 110 and managethe transfer of data on the network 110.

FIG. 2b shows components of the target server 200 ₂ as including aprocessor 202 ₂ and a memory 204 ₂ including programs executed by theprocessor 202 ₂ as well as a cache 206 ₂ to cache read and write datafor the target volume 104 ₂. The cache 206 ₂ may also store data beingtransferred between the servers 200 ₁, 200 ₂ as part of mirror copyrelationships. The memory 204 ₂ includes an operating system 208 ₂,which forms volumes 104 ₂ and maintains volume tables 210 ₂, such as avolume table of contents (VTOC), file allocation table, etc., providinginformation on the tracks or extents of tracks allocated to the volume104 ₂ and free space in the volume, as well as other metadata.

The operating system 208 ₂ may manage volumes 104 ₂ as thin provisionedvolumes and allocate space to the provisioned but unallocated space anda space release task 214 ₂ may issue commands to the device adaptors 216to release space allocated to a thin provisioned volume 104 _(i) to makeavailable to assign to other volumes 104 _(j).

The memory 204 ₂ includes a target copy manager 212 ₂ to create andmanage target mirror relationships 400 to mirror data in volumes 104 ₁in the source storage system 100 _(l) to the target volume 104 ₂ in thetarget storage system 100 ₂ as part of consistency groups. The targetmirror copy relationship information 400 provides information on sourcevolume 104 ₁ tracks copied to store at the target volume 104 ₂ of asource-target volume pair. The target copy manager 212 ₂ furthermaintains point-in-time (“PiT”) copy relationship information 500 havinginformation on a point-in-time copy of a target volume 104 ₂ that may becreated after forming a consistency group at the target volume 104 ₂.

The operating system 208 ₂ may further spawn one or more space releasetasks 214 ₂ to generate a space release list 215 indicating tracks inthe target volume 104 ₂ available for space release as indicated by asource volume table 218 sent from the source server 200 ₁ indicating astate of the tracks in the source volume 104 ₁ as of a consistency grouptime when the consistency group being formed. There may be multiplesource volume tables 218 for multiple source-volume pairs in theconsistency group being formed.

The server 200 ₂ includes one or more device adaptors 216 ₂ tocommunicate with devices in the target storage 106 ₂ and one or morenetwork adaptors 218 ₂ to communicate with the network 110 and managethe transfer of data on the network 110.

FIG. 3 illustrates an embodiment of an instance of a source mirror copyrelationship 300 _(i) maintained at the source server 200 ₁, which mayinclude a mirror copy identifier 302 identifying the mirror copy createdby a source copy manager 212 ₁; a source volume 304, such as all or partof a source volume 104 ₁, from which data is copied; a target volume306, such as all or part of a target volume 104 ₂, to which data iscopied from the source volume 304; an out-of-synch data structure 308,such as a bitmap, indicating tracks or other data units in the sourcevolume 304 that have been written, i.e., updated or changed, and need tobe copied to the target volume 306; change recording data structure 310,such as a change recording bitmap, indicating source 304 tracks thathave been updated or changed to be included in the next consistencygroup to form; a volume table copy 312 comprising a copy of a volumetable 210 at the source sever 200 ₁, which may be stored in the cache206 ₁ at the source sever 200 ₁, having a state of the tracks in thesource volume 304 as of a consistency group time; and a space releaselist 314 indicating tracks in the source volume 304 to release.

To create a new consistency group, the change recording data structure310, indicating data written, i.e., updated, while copying written datafor the current consistency group being formed, is merged with theout-of-synch data structure 308, which does not indicate tracks to copyafter the current consistency group is completed. After the merging, thechange recording data structure 310 is cleared to record new updates fora next consistency group while the data indicated as changed in theout-of-synch data structure 308 is being copied to the target volume 306to form the current consistency group.

FIG. 4 illustrates an embodiment of an instance of a target mirror copyrelationship 400 _(i) maintained at the target server 400 ₂, which mayinclude a mirror copy identifier 402 identifying the mirror copy createdby a source copy manager 412 ₁; a source volume 404, such as all or partof a source volume 104 ₁, from which data is copied; and a target volume406, such as all or part of a target volume 104 ₂, to which data iscopied from the source volume 404.

FIG. 5 illustrates an embodiment of point-in-time (“PiT”) copyrelationship information 500 for a point-in-time copy created of thetarget volume 104 ₂ when the source server 200 ₁ has completed copyingall the data indicated in the out-of-synch data structure 308 for thecurrent consistency group being formed. The source server may send apoint-in-time copy command to create the point-in-time copy 108, 500after copying all the tracks for the consistency group. Point-in-timecopy information 500 may include a PiT copy identifier 502 identifyingthe PiT copy 108 created by the target copy manager 212 ₂; apoint-in-time 504 of the PiT copy 500, such that data is consistent asof that point-in-time 504; PiT source volume 506, e.g., target volume104 ₂, from which data is copied; PiT target volume 508, e.g.,point-in-time copy 108, to which the PiT source volume data is copied;and change information 510 indicating data or tracks in the PiT sourcevolume 506, e.g., target volume 104 ₂, that needs to be copied to thePiT target volume 508, e.g., 108, such as tracks that have changed sincethe point-in-time 504 and while the PiT copy 502 was open. The changeinformation 510 may comprise a bitmap having a bit for each data unit(e.g., track) that is set to one of two values indicating the data ortrack represented by the bit has or has not been updated since thepoint-in-time 504. The source 506 and target 508 data may comprise avolume, a subset of a volume or other unit of data. When the bitindicates the track has been updated, than that track needs to be copiedto the point-in-time copy 108.

The mirror copies 300, 400 and point-in-time copies 500 may beimplemented with copy technology known in the art, such as IBM®FlashCopy®, IBM® Metro Mirror@, IBM® Global Mirror@, and mirror andsnapshot technology provided from other vendors. (IBM, FlashCopy, MetroMirror, and Global Mirror are registered trademarks or common law marksthroughout the world.

A point-in-time copy 500 replicates data in a manner that appearsinstantaneous, and any actual data transfers to the copy volume aredeferred to a later time when the data in the target volume 104 ₂ in thepoint-in-time copy 108 is subject to a write following the creation ofthe point-in-time copy. The point-in-time copy appears instantaneousbecause complete is returned to the copy operation in response togenerating the data structures 500 without copying the data.Point-in-time copy techniques typically defer the transfer of the datain the target volume 104 ₂ at the time the point-in-time copyrelationship 500 was established to the point-in-time copy 108 until awrite operation is requested to that data block on the target volume 104₂ following the point-in-time 504.

FIG. 6 illustrates an embodiment of operations performed by the targetcopy manager 212 ₂ to form a consistency group as of a consistency grouptime at a target volume 104 ₂ at the target storage 106 ₂. Uponinitiating (at block 600) an operation to form a consistency group atthe target volume 104 ₂, the target copy manager 212 ₂ receives (atblock 602) tracks from the source server 200 ₁ for the source volume 104₁ and writes the tracks to the target volume 104 ₂ of a mirror copyrelationship 300 _(i) for the consistency group.

FIG. 7 illustrates an embodiment of operations performed by the targetcopy manager 212 ₂ to process a message from the source server 200 ₁that the consistency group being formed is completed, which may comprisecreate point-in-time copy command. Upon receiving (at block 600) amessage from the source server 200 ₁ indicating that all tracks from theconsistency group indicated in the out-of-synch data structure 308 atthe source sever 200 ₁ have been copied to the target server 200 ₂, suchas may be indicated with a point-in-time copy establish command, thetarget copy manager 212 ₂ may spawn (at block 702) a space release task214 to determine tracks in the target volume 104 ₂ from the volume tablespace to release. The space release task 214 may form (at block 704) aspace release list 215 indicating tracks for space release andconstructs (at block 706) space release commands for the tracks in thespace release list 215 to send to the device adaptor 216 to execute torelease space in the target volume 406. After releasing the space, thetarget copy manager 212 ₂ creates (at block 708) a point-in-time copy108 of the target volume 104 ₂ having all the tracks for the consistencygroup just completed. The target copy manager 212 ₂ may return (at block710) complete to the source server 200 ₁ forming the consistency groupin response to completing releasing space indicated in the volume table210 as available to release and creating the point-in-time copy 108.

With the embodiment of FIGS. 6 and 7, the completion of a consistencygroup is delayed until the free space is released from the target volume104 ₂, so that unused data may be made available for other volumes in athin provisioned environment. Further, with described embodiments, thespace relations happen automatically at the copy manager of the targetserver using the most relevant and current information for the targetvolume maintained at the target server.

With the embodiment of operations in FIGS. 6 and 7, the space releaseoperations for the target volume 104 ₂ are performed at the targetserver 200 ₂ after the consistency group is formed at the target volume,which is signaled by the source server 200 ₁ sending the createpoint-in-time command. In this embodiment, the space release operationsmay not interfere with the copying of the source tracks and is performedafter the consistency group is formed so that space is released beforereturning complete to the source server 200 ₁. In an alternativeembodiment, the space release operations at blocks 702, 704, 706 of FIG.7 may be performed while the consistency group is being formed, such aswhile tracks from the source volume 104 ₁ are being copied to the targetvolume 104 ₂.

FIG. 8 illustrates an embodiment of operations performed by the targetcopy manager 212 ₂ to release space for multiple target volumes inmultiple source-target volume pairs identified in multiple mirror copyrelationships 400 ₁ . . . 400 _(n) to maintain data in the targetvolumes 406 ₁ . . . 406 _(n) consistent as of the same consistency grouptime across source-target volume pairs. The source volumes 404 ₁ . . .404 _(n) and the target volumes 406 ₁ . . . 406 _(n) in a consistencygroup may be stored in different source storage systems 100 ₁ anddifferent target storage systems 100 ₂, respectively, or the multiplesource and target volume pairs may be stored in the same source storagesystem 100 ₁ and target storage system 100 ₂. Upon the target copymanager 212 ₂ processing (at block 800) tracks from the source server200 ₁ for multiple source volumes 104 ₁ mirrored to multiple targetvolumes 104 ₂ for a new consistency group, the target copy manager 212 ₂round robin selects (at block 802) a source-target volume pair mirrorrelationship 400 _(i) from the source-target volume pair mirrorrelationships 400 ₁ . . . 400 _(n) at a target server 200 ₂ or acrosstarget servers. For each consistency group being processed, the targetcopy manager 212 ₂ selects at least one source-target volume pair, butless than all the source-target volume pair mirror relationships 400 ₁ .. . 400 _(n), to process for releasing space for the tracks from theselected at least one source-target volume pair. The target copy manager212 ₂ performs (at block 804) operations in FIG. 7 to release space forthe selected source-target volume pair.

With the embodiments of FIG. 8, when there are multiple source-targetvolume pair mirror relationships 400 ₁ . . . 400 _(n), only one, or lessthan all, of the source-target volume pair mirror relationships 400 ₁ .. . 400 _(n) is selected for space release to minimize the impact onformation of a consistency group across multiple source-target volumepair mirror relationships 400 ₁ . . . 400 _(n), because the target copymanager 212 ₂ is only delayed to release space for one of thesource-target volume pairs before returning complete to the consistencygroup to the source servers for each of the source-target volume pairmirror relationships 400 ₁ . . . 400 _(n). Otherwise, the consistencygroup would not complete until space release operations completed forall the source-target volume pair mirror relationships 400 ₁ . . . 400_(n). The embodiment of FIG. 8 allows for faster completion of completeto the create point-in-time copy command returned to the sourceserver(s) for multiple source-target volume pair mirror relationships400 ₁ . . . 400 _(n), because the space release operations of thedescribed embodiments only need to complete for a selected one orlimited number of source-target volume pairs in the consistency group.

Described embodiments provide optimizations to the computer technologyfor determining when to release space allocated to tracks in a targetvolume of a mirror copy relationships by determining space to releaseduring the mirroring of the tracks in the source volume, and releasingspace indicated in a volume table.

The reference characters used herein, such as i and n, are used todenote a variable number of instances of an element, which may representthe same or different values, and may represent the same or differentvalue when used with different or the same elements in differentdescribed instances.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The computational components of FIG. 1, including the servers 200 ₁, 200₂ may be implemented in one or more computer systems, such as thecomputer system 902 shown in FIG. 9. Computer system/server 902 may bedescribed in the general context of computer system executableinstructions, such as program modules, being executed by a computersystem. Generally, program modules may include routines, programs,objects, components, logic, data structures, and so on that performparticular tasks or implement particular abstract data types. Computersystem/server 902 may be practiced in distributed cloud computingenvironments where tasks are performed by remote processing devices thatare linked through a communications network. In a distributed cloudcomputing environment, program modules may be located in both local andremote computer system storage media including memory storage devices.

As shown in FIG. 9, the computer system/server 902 is shown in the formof a general-purpose computing device. The components of computersystem/server 902 may include, but are not limited to, one or moreprocessors or processing units 904, a system memory 906, and a bus 908that couples various system components including system memory 906 toprocessor 904. Bus 908 represents one or more of any of several types ofbus structures, including a memory bus or memory controller, aperipheral bus, an accelerated graphics port, and a processor or localbus using any of a variety of bus architectures. By way of example, andnot limitation, such architectures include Industry StandardArchitecture (ISA) bus, Micro Channel Architecture (MCA) bus, EnhancedISA (EISA) bus, Video Electronics Standards Association (VESA) localbus, and Peripheral Component Interconnects (PCI) bus.

Computer system/server 902 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 902, and it includes both volatileand non-volatile media, removable and non-removable media.

System memory 906 can include computer system readable media in the formof volatile memory, such as random access memory (RAM) 910 and/or cachememory 912. Computer system/server 902 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 913 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”). Although not shown, amagnetic disk drive for reading from and writing to a removable,non-volatile magnetic disk (e.g., a “floppy disk”), and an optical diskdrive for reading from or writing to a removable, non-volatile opticaldisk such as a CD-ROM, DVD-ROM or other optical media can be provided.In such instances, each can be connected to bus 908 by one or more datamedia interfaces. As will be further depicted and described below,memory 906 may include at least one program product having a set (e.g.,at least one) of program modules that are configured to carry out thefunctions of embodiments of the invention.

Program/utility 914, having a set (at least one) of program modules 916,may be stored in memory 906 by way of example, and not limitation, aswell as an operating system, one or more application programs, otherprogram modules, and program data. Each of the operating system, one ormore application programs, other program modules, and program data orsome combination thereof, may include an implementation of a networkingenvironment. The components of the computer 902 may be implemented asprogram modules 916 which generally carry out the functions and/ormethodologies of embodiments of the invention as described herein. Thesystems of FIG. 1 may be implemented in one or more computer systems902, where if they are implemented in multiple computer systems 902,then the computer systems may communicate over a network.

Computer system/server 902 may also communicate with one or moreexternal devices 918 such as a keyboard, a pointing device, a display920, etc.; one or more devices that enable a user to interact withcomputer system/server 902; and/or any devices (e.g., network card,modem, etc.) that enable computer system/server 902 to communicate withone or more other computing devices. Such communication can occur viaInput/Output (I/O) interfaces 922. Still yet, computer system/server 902can communicate with one or more networks such as a local area network(LAN), a general wide area network (WAN), and/or a public network (e.g.,the Internet) via network adapter 924. As depicted, network adapter 924communicates with the other components of computer system/server 902 viabus 908. It should be understood that although not shown, other hardwareand/or software components could be used in conjunction with computersystem/server 902. Examples, include, but are not limited to: microcode,device drivers, redundant processing units, external disk drive arrays,RAID systems, tape drives, and data archival storage systems, etc.

The terms “an embodiment”, “embodiment”, “embodiments”, “theembodiment”, “the embodiments”, “one or more embodiments”, “someembodiments”, and “one embodiment” mean “one or more (but not all)embodiments of the present invention(s)” unless expressly specifiedotherwise.

The terms “including”, “comprising”, “having” and variations thereofmean “including but not limited to”, unless expressly specifiedotherwise.

The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise.

The terms “a”, “an” and “the” mean “one or more”, unless expresslyspecified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

A description of an embodiment with several components in communicationwith each other does not imply that all such components are required. Onthe contrary a variety of optional components are described toillustrate the wide variety of possible embodiments of the presentinvention.

When a single device or article is described herein, it will be readilyapparent that more than one device/article (whether or not theycooperate) may be used in place of a single device/article. Similarly,where more than one device or article is described herein (whether ornot they cooperate), it will be readily apparent that a singledevice/article may be used in place of the more than one device orarticle or a different number of devices/articles may be used instead ofthe shown number of devices or programs. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments of the present inventionneed not include the device itself.

The foregoing description of various embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many embodiments of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims herein after appended.

What is claimed is:
 1. A computer program product for releasing space in a target volume to which data is copied from a source volume, wherein the computer program product comprises a computer readable storage medium having program instructions executable by a processor to cause operations, the operations comprising: writing tracks received from the source volume to the target volume to form a consistency group of tracks in the source volume at the target volume; determining tracks available to release from a volume table providing a state of the tracks in the target volume; releasing space allocated to the determined tracks; creating a point-in-time copy of the target volume; and returning complete to forming the consistency group in response to releasing the space and creating the point-in-time copy.
 2. The computer program product of claim 1, wherein the releasing the space comprises: forming a space release list indicating the determined tracks; constructing space release commands for the tracks in the space release list; and sending the space release commands to a device adaptor to execute against the target volume to release the space, wherein the returning complete is performed in response to the device adaptor completing executing the space release commands and the creating the point-in-time copy of the target volume.
 3. The computer program product of claim 1, wherein the operations further comprise: receiving a message indicating that all tracks from the consistency group have been copied to the target volume, wherein the creating the point-in-time copy is performed in response to receiving the message.
 4. The computer program product of claim 3, wherein the determining tracks available to release and releasing the space are performed in response to receiving the message, and wherein the creating the point-in-time copy is performed in response to releasing the space for the tracks available to release.
 5. The computer program product of claim 3, wherein the message comprises a command to create a point-in-time copy.
 6. The computer program product of claim 1, wherein there are a plurality of source-target volume pairs for which tracks from source volumes are copied to target volumes for the consistency group, wherein the operations of writing the tracks to the target volume, the determining tracks available to release, releasing the space, creating the point-in-time copy, and the returning complete to forming the consistency group are performed for each of the plurality of source-target volume pairs in the consistency group.
 7. The computer program product of claim 6, wherein the determining the tracks available to release and releasing the space are performed for a selected source-target volume pair of the source-target volume pairs for the consistency group, wherein the operations further comprise: alternating selecting a source-target volume pair from the source-target volume pairs across a plurality of consistency groups being formed at the source-target volume pairs; and performing the determining the tracks available to release and releasing the space for the selected source-target volume pair during the consistency groups being formed.
 8. The computer program product of claim 7, wherein the alternating selecting a source-target volume pair comprises round-robin selecting a source-target volume pair over the consistency groups to release space for a subset of at least one selected source-target volume pair less than all of the plurality of source-target volume pairs during formation of each of the consistency groups.
 9. The computer program product of claim 1, wherein the target volume comprises a thin provisioned volume, and wherein the space is released from the target volume to make available to other volumes configured in a target storage in which the target volume is configured.
 10. A system for releasing space in a target volume to which data is copied from a source volume, comprising: a processor; and a computer readable storage medium having program instructions executable by the processor to cause operations, the operations comprising writing tracks received from the source volume to the target volume to form a consistency group of tracks in the source volume at the target volume; determining tracks available to release from a volume table providing a state of the tracks in the target volume; releasing space allocated to the determined tracks; creating a point-in-time copy of the target volume; and returning complete to forming the consistency group in response to releasing the space and creating the point-in-time copy.
 11. The system of claim 10, wherein the operations further comprise: receiving a message indicating that all tracks from the consistency group have been copied to the target volume, wherein the creating the point-in-time copy is performed in response to receiving the message.
 12. The system of claim 11, wherein the determining tracks available to release and releasing the space are performed in response to receiving the message, and wherein the creating the point-in-time copy is performed in response to releasing the space for the tracks available to release.
 13. The system of claim 10, wherein there are a plurality of source-target volume pairs for which tracks from source volumes are copied to target volumes for the consistency group, wherein the operations of writing the tracks to the target volume, the determining tracks available to release, releasing the space, creating the point-in-time copy, and the returning complete to forming the consistency group are performed for each of the plurality of source-target volume pairs in the consistency group.
 14. The system of claim 13, wherein the determining the tracks available to release and releasing the space are performed for a selected source-target volume pair of the source-target volume pairs for the consistency group, wherein the operations further comprise: alternating selecting a source-target volume pair from the source-target volume pairs across a plurality of consistency groups being formed at the source-target volume pairs; and performing the determining the tracks available to release and releasing the space for the selected source-target volume pair during the consistency groups being formed.
 15. The system of claim 14, wherein the alternating selecting a source-target volume pair comprises round-robin selecting a source-target volume pair over the consistency groups to release space for a subset of at least one selected source-target volume pair less than all of the plurality of source-target volume pairs during formation of each of the consistency groups.
 16. A method for releasing space in a target volume to which data is copied from a source volume, comprising: writing tracks received from the source volume to the target volume to form a consistency group of tracks in the source volume at the target volume; determining tracks available to release from a volume table providing a state of the tracks in the target volume; releasing space allocated to the determined tracks; creating a point-in-time copy of the target volume; and returning complete to forming the consistency group in response to releasing the space and creating the point-in-time copy.
 17. The method of claim 16, further comprising: receiving a message indicating that all tracks from the consistency group have been copied to the target volume, wherein the creating the point-in-time copy is performed in response to receiving the message.
 18. The method of claim 17, wherein the determining tracks available to release and releasing the space are performed in response to receiving the message, and wherein the creating the point-in-time copy is performed in response to releasing the space for the tracks available to release.
 19. The method of claim 16, wherein there are a plurality of source-target volume pairs for which tracks from source volumes are copied to target volumes for the consistency group, wherein the writing the tracks to the target volume, the determining tracks available to release, releasing the space, creating the point-in-time copy, and the returning complete to forming the consistency group are performed for each of the plurality of source-target volume pairs in the consistency group.
 20. The method of claim 19, wherein the determining the tracks available to release and releasing the space are performed for a selected source-target volume pair of the source-target volume pairs for the consistency group, further comprising: alternating selecting a source-target volume pair from the source-target volume pairs across a plurality of consistency groups being formed at the source-target volume pairs; and performing the determining the tracks available to release and releasing the space for the selected source-target volume pair during the consistency groups being formed.
 21. The method of claim 20, wherein the alternating selecting a source-target volume pair comprises round-robin selecting a source-target volume pair over the consistency groups to release space for a subset of at least one selected source-target volume pair less than all of the plurality of source-target volume pairs during formation of each of the consistency groups. 